I design furniture everyday, however most of my assemblies are a solid color, however I have done a lot of wood grain finishes if they want to see it here or the end customer wants to see a rendering as well.
There isn't a quick easy fix when it comes to applying wood grains to an assembly. What I found works best, (providing you want to create an awesome render), is apply the wood grain at the part level not the assembly level, you would think it would be quickest to open an assembly and take the wood grain and drape it over everything, doing that creates an issue with mapping, it is much much harder to create a nice unit all the way around doing it that way. Again start at the part level and adjust the wood grain to size from there, you'll have a much better looking pc, takes more time, but nicer..
Here is a view of the Wood Grain Appearance window - Circled on the left is the settings that I use with the part in an ISO view, then you can pivot and stretch or shrink the box accordingly. You can also change or add color to make the pc lighter or darker if you want...... Again for best results start at the part level, and if you have the same part in different colors or woods, then create display states. One thing to keep in mind when applying these appearances they do show up differently in a rendering, so what you see in the SW screen will be different when rendered.. - Have fun